What are the constraints when using critical path method CPM in schedule optimization

Question

I’ve been using the Critical Path Method (CPM) for schedule optimization, but I know it has its limitations. What constraints should I watch out for when relying on CPM to manage project timelines?

Answer 1

CPM is useful for determining the longest sequence of dependent tasks, but it has several drawbacks. Here's what you should be aware of:

• Rigid Task Dependencies - CPM assumes permanent dependencies when, in practice, teams frequently work in parallel or find ways to dynamically abbreviate jobs.

• Limited Resource Consideration - It does not account for resource limits. You may have an optimum schedule, but if crucial persons or materials are unavailable, delays will occur.

• Unrealistic Float Assumptions - CPM estimates float (slack time), but this assumes that tasks' priorities do not vary, which is not always the case in dynamic contexts.

• Difficulty Handling Uncertainty - Variability in task durations is underappreciated. Unlike PERT, CPM does not take into account best- and worst-case situations.

• Ignoring External Factors - External dependencies (vendor delays, government approvals) can derail even the best-planned CPM strategy.

CPM has a solid basis, but it is most effective when combined with risk analysis and resource management to prevent bottlenecks.